Question

Calcular a soma da PA (3,6,9,...,120)

Answer 1

Sn = (a1 + an)n/2


An = a1 + (n-1)r
120 = 3 + 3N - 3
3n = 120
N = 40

S40 = (3+120).20
S40 = 123.20
S40 = 2460